This invention relates to flame retarded thermoplastic compositions and more particularly to flame retarded styrenic compositions.
As disclosed in many U.S. patents, of which U.S. Pat. No. 4,107,232 is representative, it is known to use polytetrafluoroethylene (PTFE) resin as an anti-drip agent in polymeric compositions containing flame retardant additives. It is also generally known that the performance properties of such compositions can be adversely affected at additive levels therein required to achieve a satisfactory degree of flame retardant performance as measured by published standards such as The Underwriters Laboratory flammability test, designated UL 94. For example, the levels of flame retardants in a polymeric ABS composition (a copolymer of styrene and acrylonitrile grafted on a rubber substrate which is dispersed in an ungrafted matrix copolymer of styrene and acrylonitrile) necessary to achieve a UL 94 rating of V-0 (as hereinafter defined) can result in bloom and/or plateout problems when the composition is molded into parts. As used herein, "bloom" means the undesirable appearance of a white layer of material on the surface of a flame retarded molded part after a period of time as short as a few minutes. The layer is principally composed of flame retardant additive(s) which have migrated to the surface of the part. The term "plateout" as used herein, means the deposition and buildup of material on the surface of a mold being used to shape parts made from such composition, which material is transferred to the parts causing surface appearance defects, and which can plug mold vents to cause molding problems from trapped gases; the built up material is principally composed of the flame retardant additive(s) used in the specific molding composition. Moreover, such high levels of flame retardant additives can result in a deterioration of the strength properties of the composition in comparison with those of the unmodified material.